Fish problem

chris lawrence clawrenc at
Wed Jan 14 14:17:48 EST 2004

your fish are indeed killing one another overnight.  this is common, 
especially when you are setting up pairwise crosses.  for whatever 
reason, one fish may be aggressive towards the other (the male or 
female can be the aggressor) and when you put them together in a 
small space with nowhere to hide, you will almost always have either a 
battered or dead fish in the tank in the am after a night of constant 
violence.  some individuals seem to be more aggressive and 
predisposed to this type of behavior than others. the easiest way to 
prevent this is to separate the fish overnight with a divider, and then 
simply pull it in the am when the lights go on.  this will take care of 
most of your problems, as long as you don't leave them together for 
more than an hour or two and/or you monitor the situation to see that 
no abuse is taking place.  

if you don't want to use dividers, you can assess the situation within 
minutes after you set the pair up.  watch for aggressive behavior - 
constant chasing, attacking, extended fins, etc.   this could arise 
overnight, but more often than not, you will see it as soon as the fish 
get accustomed to their surroundings..  if you see this, divide them or 
mix and match individuals (if you can).  sometimes the chemistry 
between two individuals just isn't right.  

Christian Lawrence
Havard Biological Laboratories
Zebrafish Facility
16 Divinity Avenue
Cambridge, MA 02138
Tel: 617.496.8193
Fax: 617.495.3321
clawrenc at


"Christina Quasarano" <ceq at> wrote in message
news:bu3pr7$mq3$1 at
> Hello all,
> My lab is having a little problem with our AB fish.  In the past
> week 3 of our very few AB fish have died, and in no way I have ever
> seen or heard of before.  What the situation has been is that these
> fish are in mating tanks as couples (1M/1F) and in the morning one
> of them is dead.  It looks like the scales and top layer of flesh on
> parts of the
> has dissappeared or disintegrated right down to the muscle tissue.
> What might be causing this?  Could the other fish be attacking the
> other? Or nibbling at the dead/sick one?  Any suggestions would
> help. Thank you!
> Sincerely, Christina
> ***************************************
> Christina Quasarano
> Lab Manager <}}}><
> Chemical Hygiene Officer
> Lab of Sleep and Circadian Physiology
> Department of Anatomy and Neurobiology
> Phone # (617)638-4187
> ---


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